a) Field of the invention:
The present invention relates to a shutter for cameras, and more particularly a braking means which is suited for use with focal plane shutters.
b) Description of the prior art:
Certain shutters for cameras are equipped with braking means which serve for preventing shutter blades and shutter blade actuating members from rebounding at the time of opening or closing operations of the shutter blades. An ordinary type of the braking means for focal plane shutters adopts a brake lever utilizing frictional plates and is configured so as to exert a braking force to the shutter blade actuating member by bringing the shutter blade actuating member into contact with the brake lever at a final stage of a movement of the shutter blade actuating member (Japanese Utility Model Preliminary Publication No. Sho. 60-68523). Further, another type of the braking means for focal plane shutters comprises an elastic member disposed in a final region of a moving course for the shutter blade actuating member and is configured so as to exert a braking force to the actuating member by bringing the actuating member into contact with the elastic member at the final stage of the movement of the actuating member (Japanese Utility Model Preliminary Publication No. Sho 56-88227). Furthermore, still another type of the braking means for focal plane shutters adopts, in place of the elastic member described above, a horseshoe-shaped member made of an elastic material and is configured so as to exert a braking force to the shutter blade actuating member by fitting or receiving a pin formed integrally with the shutter blade actuating member into or with the horseshoe-shaped member at the final stage of the movement of the shutter blade actuating member (Japanese Patent Preliminary Publication No. Sho 59-210424). The braking means of the types described above pose a common problem that these braking means require stronger forces for moving the shutter blade actuating members in the reverse direction to cock the shutters as these means exert stronger braking forces. Moreover, these braking means pose another problem that these means allow the braking forces to be weakened and/or made unstable after long-term use due to abrasion of the frictional plates and the elastic members. In addition, the braking means of the types described above have a common defect that costs required for manufacturing focal plane shutters are increased by these braking means.
There is additionally known a different type of braking means which is configured so as to exert a biasing force to the braking lever by utilizing a coil spring. This braking means is constructed so as to allow a restoring force of the coil spring to be exerted to the shutter blade actuating member when the brake lever is pushed by the actuating member at the final stage of the movement of the shutter blade actuating member. As a braking means of a type which is similar to the braking means disclosed by the Japanese patent mentioned above, there is also known a braking means which is configured so as to allow the restoring force of the coil spring to be exerted directly to the shutter blade actuating member. Unlike the braking means which utilize the frictional plates or the elastic members, the braking means of the last two types are capable of maintaining stable operations even after long-term use, but apt to allow high-speed rebounds of the shutter blade actuating members and the shutter blades at the stopping time thereof, and therefore require lock levers for preventing the rebounds of the actuating members and the shutter blades. Accordingly, each of these two types of braking means requires a mechanism which is to be used for releasing the lock lever before cocking a shutter and has a defect the braking means is inevitably complicated in the structure thereof. Further, the braking means utilizing the coil springs has another defect that these means can hardly control a timing for locking the shutter blade actuating members by using the lock lever since the timing is variable dependently on lapse of time and variations of ambient conditions such as temperature.